Misconvergence compensation for single-gun, plural-beam-type color tv picture tube

ABSTRACT

A single-gun, plural-beam-type color television picture tube in which three electron beams representing different color signals are focused by a single lens, after which two of the beams diverge. The two divergent beams are reconverge by convergence deflecting means so they will intersect with the third beam at a common point at a beam-selecting grid, from which point the beams again diverge to impinge on respective color phosphors which together represent a color picture element. Misconvergence, i.e., reconvergence of the two divergent beams to a point other than to the common point of intersection with the third beam, which arises from manufacturing inaccuracies such as the misorientation of the convergence deflecting means with respect to the single electron gun of the tube, or the misorientation of the aperture of the beam-generating means of the tube, is compensated for by the provision of convergence deflecting means which exerts upon at least one of the divergent beams an electric, or Coulomb, force which varies in its direction in accordance with the position at which the beam enters and passes through the convergence deflecting means. Thereby, variations in the direction of the electric force compensates for variations in the position at which the beam is introduced to eliminate the misconvergence which arises from the above-mentioned manufacturing inaccuracies.

United States Patent [72] Inventors Senri Miyaoka Kanagawa-ken; MinoruMorio, Tokyo, both of Japan [21] Appl. No, 815,870 22 Filed Apr. 14,1969[45] Patented Oct. 19, I971 [73] Assignee Sony Corporation Shinagawa-ku,Tokyo, Japan [32] Priority Apr. 14, 1968 [33] Japan [31 43/24897 [54]MISCONVERGENCE COMPENSATION FOR SINGLE-GUN, PLURAL-BEAM-TYPE COLOR TVPICTURE TUBE 4 Claims, 11 Drawing Figs. [52] US. CI 313/69 C, 313/78 [51Int. Cl ..H0lj 29/02, H01j31/20, HOlj 29/74 [50] Field of Search 313/70C, 78, 80

[56] References Cited I UNITED STATES PATENTS 2,148,588 2/1939 Snow313/78 X 2,197,523 4/1940 Gabor 313/78 X 2,849,646 8/1958 Noskowicz313/78 X 2,911,563 11/1959 Atti et 313/78 X 3,124,790 3/1964 Kuehler313/80 X 3,448,316 '6/1969 Yoshidaetal. 313/70CX 3,462,638 8/1969Tetsuoetal. 313/70 CX 3,497,744 2/1970 Himmelbaueretal. 313/78 PrimaryExaminer-Robert Segal Attorneys-Albert C. Johnston, Robert E. lsner,Lewis H.

Eslinger and Alvin Sinderbrand ABSTRACT: A single-gun, plural-beam-typecolor television picture tube in which three electron beams representingdifferent color signals are focused by a single lens, after which two ofthe beams diverge. The two divergent beams are reconverge by convergencedeflecting means so they will intersect with the third beam at a commonpoint at a beam-selecting grid, from which point the beams again divergeto impinge on respective color phosphors which together represent acolor picture element. Misconvergence, i.e., reconvergence of the twodivergent beams to a point other than to the common point ofintersection with the third beam, which arises from manufacturinginaccuracies such as the misorientation of the convergence deflectingmeans with respect to the single electron gun of the tube, or themisorientation of the aperture of the beam-generating means of the tube,is compensated for by the provision of convergence deflecting meanswhich exerts upon at least one of the divergent beams an electric, orCoulomb, force which varies in its direction in accordance with theposition at which the beam enters and passes through the convergencedeflecting means. Thereby, variations in the direction of the electricforce compensates for variations in the position at which the beam isintroduced to eliminate the misconvergence which arises from theabove-mentioned manufacturing inaccuracies.

PAIENIEnnm 19 l97l SHEET 2 OF 2 I NV EN TORS SENRI MIYAOKA MINORU MORIOI ATTORNEY MISCONVERGENCE COMPENSATION FOR SINGLE- GUN, PLURAL-BEAM-TYPECOLOR 'IV PICTURE TUBE This invention relates generally to color picturetubes of the single-gun, plural-beam type, and particularly to tubes ofthat type in which the plural beams are passed through the opticalcenter of a common electron lens by which the beams are focused on thecolor phosphor screen of the tube.

A single-gun, plural-beam color picture tube exists, in which threedifferent cathodes produce three different electron beams thatrespectively correspond to the three primary colors. An example of sucha tube is disclosed specifically in a copending U.S. application Ser.No. 697,414 filed Jan. 12, I968, Pat. No. 3,448,316 and having a commonassignee herewith. The cathodes in such a tube are arranged in ahorizontal row, so that the three electron beams start out side by side.Shortly after leaving the gun, the three beam intersect at a commonpoint in the center of a single electrostatic lens which serves to focusall three beams upon a color screen. However, after leaving the focusinglens, the three electron beams diverge. The center beam continues in acentral straight line, but the two beams on both sides divergesidewardly, i.e., outwardly, away from the path of the central beam, andmust therefore be reconverged by pairs of convergence deflectionelectrodes to which a convergence deflection voltage is applied. Thisconvergence causes all three beams to intersect at a common point wherethey pass through a beamselecting grid, after which they again divergeto impinge on the respective color phosphors constituting a colorpicture element on the color screen.

The pairs of convergence deflection electrodes in the picture tube shownand described in this copending application comprise plates which aredisposed in parallel with each other. Since the electrodes, i.e.,plates, are flat and parallelly disposed with respect to each other, thedirection of the electric, or Coulomb, force applied to the electronbeams is always at right angles to the surface of these plates. As aresult, misconvergence, i.e., reconvergence of the two divergent beamsto a point other than the common point of intersection with the thirdbeam, can be prevented only if the plural beam (i.e., the beamcomprising the three beams mentioned above) always is introduced intoconvergence deflection electrodes at a predetermined position. If,because of manufacturing inaccuracies, this predetermined position isdeviated from by a shift of the beam with respect to the plates or byanother discrepancy, which causes at least one of the two divergingbeams to be displaced in a direction parallel to surface of the flatplates, misconvergence is produced, which is not corrected by suitablycompensating for the shift or other discrepancy. The manufacturinginaccuracies which may cause this misconvergence include misorientationof the convergence deflecting means with respect to the single electrongun or misorientation of the aperture of the beam-generating means insuch a picture tube.

Accordingly, it is an object of this invention to provide a single-gun,plural-beam color picture tube of the type described in which, when adiscrepancy develops in the position at which the beams enter theconvergencedeflecting means, this discrepancy is compensated to therebyprevent misconvergence.

It is another object of this invention to provide a single-gun,plural-beam color picture tube of the type described having aconvergence deflecting means of relatively simple structure providedbetween the focusing lens and the beam-selecting grid, or mask, forcausing the beams emerging from the focusing lens along divergent pathsto converge to a point at the grid, or mask.

In a color picture tube of the type described above, the presentinvention provides convergence-deflecting means which exerts upon atleast one of the diverging beams an electric force whose directionvaries with the position at which it enters the convergence deflectingmeans, whereby any variation in the position at which it enters iscorrected, or compensated for, by a variation in the direction of theelectric force which is applied to it, such being to correct formisconvergence which would otherwise result.

The above, and other objects, features and advantages of the invention,will be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawing.

In the drawing:

' FIG. 1 is a horizontal sectional view schematically showing asingle-gun, plural-beam color picture tube such as disclosed in theabove-mentioned application;

FIG. 2 is a cross-sectional view, also schematic, taken along the lineI-I in FIG. I, which illustrates the condition when there is nodiscrepancy in the position at which the electron beams enter theconvergence-deflecting means;

FIG. 3 is a view identical to the one shown in FIG. 2 which illustratesthe condition when there is a discrepancy in the position at which twoof the electron beams enter the convergence-deflecting means;

FIG. 4 is another view identical to the one shown in FIG. 2 whichillustrates the condition when there is a discrepancy in the position atwhich one of the electron beams enters the convergence-deflecting means;

FIG. 5 is a cross-sectional view, similar to the cross-sectional view ofFIG. 2, also schematic, showing electron beam convergence deflectingmeans for use in a color picture tube identical to the one shown in FIG.1 except wherein the electron beams are disposed within the tube in adelta formation;

FIG. 6 is a perspective view schematically showing an electron beamconvergence deflecting means, constructed in accordance with theteachings of this invention, for a single-gun, plural-beam color picturetube such as shown in FIG. 1;

FIG. 7 is a cross-sectional view, taken along the line II-II in FIG. 6,which illustrates the condition when there is no discrepancy in theposition at which the electron beams enter the convergence deflectingmeans;

FIG. 8 is a cross-sectional view, identical to the one shown in FIG. 7,which illustrates the condition when there is a discrepancy in theposition at which two of the electron beams enter theconvergence-deflecting means;

FIG. 9 is a cross-sectional view, identical to the view of FIG. 7, whichillustrates the condition when the electron beams are disposed in adelta formation as they are in FIG. 5;

FIG. 10 is a view, identical to the one shown in FIG. 8, of electronbeam convergence-deflecting means constructed in accordance with andillustrating another embodiment of this invention; and

FIG. 11 is a view, similar to the one shown in FIG. 8, of still anotherelectron beam convergence-deflecting means constructed in accordancewith and illustrating still another embodiment of this invention.

Throughout these Figures the same reference characters are used to referto the same elements.

Referring to the drawings in detail, and initially to FIG. I thereofwhich schematically shows a cross-sectional view of a single-gun,plural-beam color picture tube such as disclosed in the aforementionedcopending US. application, it will be seen that a single electron gun Aof such a color television picture tube comprises three cathodes K K andK,, which produce the electron beams B B G and B respectively for thered, green and blue signals of such a tube. Thesethree beams, afterleaving their respective cathodes, pass through respective apertures g gand g fonned in a first grid 6,. Then, they proceed throughcorresponding respective apertures g and g fonned in a second grid G,The apertures of the grids G and G serve the conventional beam-formingfunction. As the electron beams leave the second grid G they then passthrough three open-ended tubular grids or electrodes G G, and G in thatorder. The grid G, and electrodes G, cooperate to form a relatively weakauxiliary lens I. by which the parallel beams are made to converge atthe optical center ofa main lens L formed by electrodes (3,, G, and Gand which serves to focus all three beams upon the phosphor screen S onthe faceplate of the tube.

After the three beams B B and B leave focusing lens L, center beam Bcontinues in a straight line coincident with-the optical axis of thelens. The beams B and B however, diverge away from the center beam BAccordingly, convergence deflecting electrodes generally designated Fare provided for the purpose of converging the outer beams to intersectat a common spot with the center beam so that all three beams passthrough the same aperture between individual grid wires g, of thebeam-selecting grid or mask 6,. Thereafter the beams again diverge sothat the red signal beam B goes on to strike the red phosphor stripe Sthe blue signal beam B goes on to strike the blue phosphor strip 8,, andthe green signal beam B goes on to strike the green phosphor stripe S ofa common color television picture element.

As indicated in FIG. 1, the first grid G may receive a static potentialof O to minus 400 volts, for example about minus 400 volts, the secondgrid G may receive a static potential of to 500 volts, for example about500 volts, while the center lens element G. may receive a potential of 0to 400 volts, for example about 400 volts. The two outer lens elements Gand G are connected to a potential V which is at or near the anodepotential (13 to 20 kv.) of the tube. The first grid G performs theintensity modulation function, and therefore also has a signal voltageapplied thereto. As a result, the voltage distributions between therespective electrodes and cathodes and the respective lengths anddiameters thereof, may be substantially identical with those of aunipotential-single-beam type electron gun which is constituted by asingle cathode and first and second, single-apertured grids. A voltage Vis applied to the grid wires g of the beam-selecting grid G Moreover, inthe conventional manner, the electron beams are swept horizontally andvertically across screen S to produce the usual cathode-ray tube raster-In FIG. 1, the electron beams B,,, B and B are swept from one extremityof the screen S to its other extremity. The horizontal and verticaldeflections necessary to produce the picture raster are of courseaccomplished by conventional deflection yokes D mounted outside the neckN of the picture tube.

In order to converge the electron beams, the electron beam convergencedeflecting means F comprises outer electrodes or flat plates, 0 and Q,and inner electrodes or flat plates P and P which are spaced from eachother and respectively spaced inwardly from the plates Q and Q. Theinner electrodes P and P are maintained at a higher potential theneither of the outer electrodes Q and 0. Since the electrodes P and P areof the same potential, the green signal beam 8 is not deflected inpassing therebetween. The blue signal beam B passes between the outerelectrode Q and the inner electrode P, while the red signal beam Bpasses between the outer electrode Q and the inner electrode P.Accordingly, the divergent beams B and B are deflected inwardly byelectric, or Coulomb, forces E and B (see FIG. 2), which are given bythe respective voltage gradiations between their respective pairs ofelectrodes Q, P and Q, P, to intersect with beam B at a common point onthe beam-selecting grid G In order to maintain the necessary highpotential upon the inner electrodes P and P, these electrodes areconnected jointly to the highest potential of the tube, i.e., the anodevoltage V,..

In order to maintain the outer electrodes 0 and Q at a somewhat lowerpotential than the inner electrodes P and P, the outer electrodes 0 andQ are provided with potential V It is sufficient that this potential Vis lower than the anode voltage V,. by about 200-300 volts.

Referring now to the convergence-deflecting means F in detail, by meansof electric force E applied to beam B, by electrodes P and Q' and bymeans of electric force E applied to beam 3,, by electrode P and Q,beams B and 18,; are deflected toward the central axis 3,; of the colorpicture tube. This axis B lies in the path defined by the beam B whichbeam, accordingly passes therealong. The beams B 8,, and B as shown inFIG. 2, are disposed in line with the horizontal axis x (i.e., they arealigned to meet if deflected at right angles to the central axis B andare introduced into the electrodes F at equal distances from each other.Accordingly, the convergence deflecting means F causes beams B,; B andB, to intersect at a common point on the beam-selecting grid G When thebeams are positioned as shown in FIG. 2, the three beams can be made tointersect accurately at the abovementioned common point by adjusting theintensity of the electric forces E and E and by adjusting the potentialV because both of the electric forces E and E are in the direction ofthe horizontal axis x-and are directed toward the beam B On the theother hand, when the coaxially disposed convergence deflecting means Fand the single electron gun A are misaligned because one is rotated,i.e., angularly displaced, out of proper position with respect to theother, because of manufacturing inaccuracies or the like, the electricforces E and E are prevented from being directed toward the beam 8,,-because, as can be seen in FIG. 3, the line a, along which beams B B and3,, are arranged, is displaced from axis x by an angle 41. Consequently,beams B B and B, are at best converged in a line along the vertical axisy, meeting at right angles with the horizontal axis x and passingthrough the central axis B when forced to converge in the direction ofthe forces E and E. They are not converged at the above-mentioned commonpoint. In addition, the respective distances between beam B and axis xand between beam B and axis x gradually increases as the beams gothrough the convergence deflecting means F toward the beam-selectinggrid 6,. In short, convergence deflecting electrodes F, shown in FIGS. 2and 3, cause deflection of the beams only in the direction of thehorizontal axis x. They do not cause the beams to be deflected in thedirection of the vertical axis y.

FIG. 4 is a cross-sectional view identical to the one shown in FIG. 3but one in which the position of the beams, at entry and upon passingthrough the deflecting means F, is somewhat different then the positionof the beams in FIG. 3. In this view, beams B and B enter and passthrough the deflecting means at a predetermined position along thehorizontal axis x, but the beam B enters and passes through at aposition on a line displaced by an angle a from the axis x, as shown inFIG. 3. The deflecting means F can focus the beams 3 and B,respectively, but it cannot focus beam B This is because there is nocomponent of electric force E in the direction of axis y to shift thebeam 8,, in that direction.

FIG. 5 is a cross-sectional view, similar to FIG. 2, of electron beamconvergence deflecting means for a single-gun, plural-beam color picturetube, such as disclosed in the aforementioned copending application,having arrays of beamemitting cathodes and color phosphor respectivelydisposed in a delta formation. In this flgure, the common innerelectrode P of the convergence deflecting means F may be in the form ofa tube having a triangular, or deltoid, cross section which is coaxialwith the optical axis of the focusing lens L, and which has three flatsides arranged parallel to the flat plates Q. Q' and O" which are spacedoutwardly therefrom. In this case also, when voltage V is applied toinner electrode P" and a relatively smaller voltage V is applied toplates 0, Q and Q", the respective beams passing therebetween aredeflected inwardly toward the central axis for convergence at a commonpoint on the beam-selecting grid G In addition, color screen 8(reference being bad to FIG. I) has, in this case, delta arrays of colorphosphor 8,, S and S and the tube has beam-selecting means 0,. andbeam-generating means respectively provided with apertures and cathodesK K and K corresponding to said arrays. Consequently, if beams B B and Bpass through a position on the axis lines x,, x, and x which linesintersect at the central line of the color picture tube and areperpendicular to the respective electrode plates 0, Q and O, theelectric forces E, E and E" applied to the respective beams B B and 8,,by the electrodes P", Q, Q and Q" are directed toward a point 0 on thecentral line. This enables the three beams to be focused on screen S. Onthe other hand if beam B for example, is biased for some reason from itsposition on axis x to a position B',,-, because of a discrepancy in theposition of apertures g and g for example, there is no possibility thatthe three electron beams B B and B will converge into the central lineof the color picture tube because the electric force E has no componentin a direction at right angles to the axis x,.

Stated succinctly, with the convergence deflecting means F shown in FIG.2 or FIG. 5, it is possible to converge the beams to correct deviationsof the beams in the directions of the axis x or the axes x x and x,, butit is impossible to converge the beams to correct deviations of thebeams in the directions at right angles with these axes thereby tocorrect, or compensate for, misconvergence. Consequently, when there isno error in design or assembly it is possible to avoid blooming of thefocused beams at a spot, such blooming being caused by sphericalaberration coma, or the like. Also it is possible to minimize the radiusof the neck of the tube and to make the deflecting power small becausethe magnetic field effect is good. On the other hand quite accuratedesign and assembly is required, the allowable error for such beinglimited to fall with a small range. Manufacturing within this limitedrange is troublesome.

In accordance with this invention convergence deflecting means F isprovided which eliminates the aforementioned troublesome manufacturingrequirements and which is designed to effectively correct for anydiscrepancy in the position at which the electron beams enter theconvergence deflecting means and to insure that the plural beams areconverged in the vicinity of the phosphor screen, for example at thebeam-selecting grid.

FIGS. 6 to 3 illustrate one embodiment of a convergence deflecting meansF constructed in accordance with the teachings of this invention for usein a single-gun, plural-beam color picture tube of the type shown inFIG. 1. Such a color picture tube, constructed in accordance with thisinvention, therefore, is either identical or similar to the tube shownin FIG. 1, except that the structure of the convergence deflecting meansF is different. This convergence deflecting means F consists of apair ofcylindrical electrodes P and O which are coaxially disposed and havedifferent radii respectively. In accordance with this construction, ifthe positions B B and B at which the electron beams B B and B enter theconvergence-deflecting means are arranged at equal intervals alonghorizontal axis x as shown in FIG. '7 (as they also are in FIG. 2), andif the electric forces E and E applied to the beams B and B by theelectrodes P and Q are directed toward the central axis B the beams B Band 8,; will be directed towards the beam B so that, as in the caseillustrated in FIG. 2, the beams B B and 8,, will accurately converge ata common point on beam-selecting grid G,,.

If the position B B and B shown in FIG. 8 at which the electron beamsenter into the convergence deflecting means F, are arranged in line adisplaced by an angle car from the horizontal axis x, as in the caseillustrated in FIG. 3, the direction of electric forces E and E appliedto beams B and 8,, will not be parallel with axis x, but will be in thedirection of the line a and directed toward the beam B As a result,electric forces E and E not only have components Ex and E): respectivelydirected towards the axis x, but also have components By and E'ydirected toward the axis y, so that, unlike in the case illustrated inFIG. 3, it is possible to converge the three beams accurately at theabove-mentioned common point. In addition, it is easy to converge thebeams since, as the an le 12 becomes larger, the components E x and Exin the direction of the axis x become smaller and the components 531 andE'y become larger. Furthermore, it should be noted that the directionsof the electric forces E and E gradually change in accordance with thechange in the angle a and that this change is made in the directionwhich provides for the accurate convergence of the beams.

As shown in FIG. 3, the beams B B and B are converged although they arenot all in a line (beam 8,, being located at the position 8' on axis x,similar to its location in FIG. 4) because the beam B is deflected inalmost the same manner as it is in FIG. '7 and beam B is displaced asdescribed above.

FIG. 9 shows convergence-deflecting means identical in construction tothe convergence means shown in FIGS. 6 to 8, but in this case it is usedfor converging electron beams that are disposed in a delta formationsuch as shown in FIG. 5. In this case, if the beams B B and B areintroduced accurately, i.e., introduced so as to define apexes of anequilateral triangle, into the convergence-deflecting means F and if theelectric forces E and E from plates P and Q are directed toward thecenter 0, as in the case shown in FIG. 5, the three electron beamsconverge. However, for some reason the electron beam B is caused to moveinto position B on line a displaced by an angle a from axis X the beam Bwill converge with the other two beams B and B almost in the same manneras either of the beams B or B converge in FIG. 8, since electric forceE' applied to beam B' has a component E"x-in the direction of axis x,and a component E"'y in the direction of axis x FIG. Ill showsconvergence-deflecting means constructed in accordance with theteachings of this invention and illustrating another embodiment of it.As shown in this figure, the electrodes P and Q respectively arenotched, i.e., they have portions removed, along their sides.Accordingly, the single electrode P of the convergence-deflecting meansshown in FIGS. 6 through 8 is substituted for a pair of opposing,halfcylindrical electrodes Q and Q". In the case when the electron beamsare disposed in the tube in a straight line, this electrode arrangementenables unnecessary portions of electrodes P and Q to be removed sincethe electron beams are not usually biased very far from horizontal axisx. This simplifies the apparatus. Furthermore, thisconvergence-deflecting arrangement achieves the same effect as isachieved by the arrangement shown in the FIGS. 6 to 8.

FIG. 11 shows other convergence-deflecting means constructed inaccordance with the teachings of this invention and illustrating stillanother embodiment of it. In this figure, the radial center point 0 ofthe electrodes P and Q are shifted respectively along axis 1: so thatthe electrodes are brought closer together. Also, the electrodes aresomewhat flatter i.e., they have less curvature, than those shown inFIG. 10. Consequently, the electric forces E and E applied respectivelyto electron beams B and B have a larger component in the direction ofthe horizontal axis x as compared to the component they have in thedirection of vertical axis y than they have in the embodiment shown inFIG. 10. Since the electric forces E and E applied to the beams B and Bare introduced on line a meeting at an angle a with the horizontal axis1:, they have components By and E'y in the direction of vertical axis yat all times. Dependent upon the particular structure of the colorpicture tube, it is often possible to converge the beams moreeffectively with this convergence-deflecting means than it is with themeans shown in FIG. 10.

The convergence-deflecting means described in detail herein haveillustrated the converging of three electron beams only, but it shouldbe understood that any number of beams, for example, 2, 4 or 5, may beconverged with apparatus constructed in accordance with the teachings ofthis invention.

In addition, beam-selecting grid G may be a chromatrontype grid (i.e., aline grid), a shadow mask, an aperture grid, any other appropriatedevice.

Although illustrative embodiments of this invention have been describedin detail herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments. and ihal Various changes and modifications may be effectedtherein by one skilled in the art without departing from the scope orspirit of the invention as defined in the appended claims.

What is claimed is:

l. A single-gun, plural-beam color picture tube which includes a colorscreen having in-line arrays of different color phosphors,beam-selecting means provided with apertures corresponding respectivelyto said arrays, beam-generating means for directing a central electronbeam and two side electron beams from in-line sources toward said colorscreen for 7 impingement on respective phosphors of each array throughthe corresponding aperture, single lens means for focusing said electronbeams on said color screen and having an optical center through whichsaid beams all are passed with said central beam being coincident withthe optical axis of said lens means and said side beams being angledwith respect to the optical axis of said lens means so as to enter saidlens means along paths that are convergent to said optical axis and toemerge from said lens means along paths that are divergent to said axis,and convergence-deflecting means interposed between said lens means andsaid beam-selecting means and being operative to deflect said side beamsemerging along said divergent paths to converge them with said centralbeam at an aperture of said beam-selecting means, saidconvergencedeflecting means comprising inner and outer electrodes whichare parallelly curved about said axis and spaced from each other andfrom said axis so that only said side beams emerging along saiddivergent paths pass between said inner and outer electrodes, and meansfor applying different potentials to said inner and outer electrodes,respectively, and thereby establishing an electric field therebetweenwhich exerts on said side beams passing therebetween forces directedsubstantially radially toward said axis irrespective of the positions atwhich said side beams enter said electric field.

2. A single-gun, plural-beam color picture tube as described in claim 1,wherein said electrodes are cylinders which are coaxially disposed andwhich have difierent radii respectively.

3. A single-gun, plural-beam color picture tube according to claim 1, inwhich an individual set of said inner and outer electrodes is providedfor each of said side beams, and said inner and outer electrodes of eachset are half-cylindrical with different radii and are coaxial with saidoptical axis.

4. A single-gun, plural-beam color picture tube according to claim 1, inwhich an individual set of said inner and outer electrodes is providedfor each of said side beams, said inner and outer electrodes of each setare part-cylindrical with different radii and have axes that are offsetfrom said optical axis in the direction away from the side of saidoptical axis at which the respective set of electrodes is disposed.

1. A single-gun, plural-beam color picture tube which includes a colorscreen having in-line arrays of different color phosphors,beam-selecting means provided with apertures corresponding respectivelyto said arrays, beam-generating means for directing a central electronbeam and two side electron beams from in-line sources toward said colorscreen for impingement on respective phosphors of each array through thecorresponding aperture, single lens means for focusing said electronbeams on said color screen and having an optical center through whichsaid beams all are passed with said central beam being coincident withthe optical axis of said lens means and said side beams being angledwith respect to the optical axis of said lens means so as to enter saidlens means along paths that are convergent to said optical axis and toemerge from said lens means along paths that are divergent to said axis,and convergence-deflecting means interposed between said lens means andsaid beam-selecting means and being operative to deflect said side beamsemerging along said divergent paths to converge them with said centralbeam at an aperture of said beam-selecting means, saidconvergencedeflecting means comprising inner and outer electrodes whichare parallelly curved about said axis and spaced from each other andfrom said axis so that only said side beams emerging along saiddivergent paths pass between said inner and outer electrodes, and meansfor applying different potentials to said inner and outer electrodes,respectively, and thereby establishing an electric field therebetweenwhich exerts on said side beams passing therebetween forces directedsubstantially radially toward said axis irrespective of the positions atwhich said side beams enter said electric field.
 2. A single-gun,plural-beam color picture tube as described in claim 1, wherein saidelectrodes are cylinders which are coaxially disposed and which havedifferent radii respectively.
 3. A single-gun, plural-beam color picturetube according to claim 1, In which an individual set of said inner andouter electrodes is provided for each of said side beams, and said innerand outer electrodes of each set are half-cylindrical with differentradii and are coaxial with said optical axis.
 4. A single-gun,plural-beam color picture tube according to claim 1, in which anindividual set of said inner and outer electrodes is provided for eachof said side beams, said inner and outer electrodes of each set arepart-cylindrical with different radii and have axes that are offset fromsaid optical axis in the direction away from the side of said opticalaxis at which the respective set of electrodes is disposed.